Which of the following blood collection tubes is used for hematology tests?

The purple or lavender tube is specifically designed for hematology tests because it contains the anticoagulant EDTA (ethylenediaminetetraacetic acid). EDTA works by binding calcium in the blood, which prevents clotting. This is crucial for hematological analysis, as it allows for accurate measurements of various blood components, including red and white blood cells, hemoglobin, and platelets, without the interference that can be caused by clotted samples.

In contrast, the other tubes all have different additives or purposes: the green tube typically contains heparin, which is also an anticoagulant but more suitable for certain chemistry tests rather than hematology; the blue tube contains citrate, which is primarily used for coagulation studies; and the red tube is generally used for serum tests as it may be used without additives or with a clot activator, which is not suitable for hematological testing.